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Stonefly emergence has already started with rising water temperature

Summer, or at least the heat of summer, arrives in force this week with temperatures across western Colorado forecast to reach the mid-90s.

What snow wasn’t dispersed during the blast of hot winds last month is sure to disappear with the coming heat.

And although you patiently wait for the stonefly hatch on the Gunnison, heat, or at least water temperature, should be where you’re focusing this week.

Among the theories of why and when the much-awaited stonefly (pteronarcys californica) hatch occurs include thoughts on moon phase, runoff rates, and air and water temperatures.

Perhaps the latter are the more important pieces to this puzzle.

The stonefly hatch hasn’t yet happened on the Gunnison. But reports from Division of Wildlife researcher Barry Nehring on the Colorado River near Parshall indicate the hatch there has already started.

He’s also reported, via Bob Burk at Cimarron Creek fly shop in Montrose, that water temperatures in the Colorado reached the critical 52-degree mark.

But it’s not just reaching 52 degrees, it’s staying at that temperature for 24 hours that might be the real key to stonefly emergence.

“Barry’s counting (stonefly) shucks in the grass and said the bugs came off really heavily last weekend,” Burk said Friday morning. “He has a temperature graph on the river there and said the water was over 52 degrees for a full 24-hour period.”

But when additional runoff dropped the water temperature, the hatch dropped, too, Burk said.

“He went from counting, say, 8,000 shucks in 50 feet to counting 200,” said Burk, who has been weighing the many variables in trout fishing for more than 20 years.

If water temperature is so important, it might explain why in some years there’s a predictable hatch progression up river while in other years it’s more of an all-out emergence everywhere you go.

“We’ve had these situations where the hatch ‘flashed’ the river in one fell swoop and all at once the whole river is ablaze with stoneflies,” Burk said.

If the air temperature is high enough this weekend to raise water temperatures to 52 degrees, and keep it there for 24 hours, the stonefly hatch might begin in earnest this week.

But staying there for 24 hours is key, Burk said.

“It was 53 degrees in Ute Park Sunday and on Monday it was 52 at the Forks,” he said. “But it didn’t stay there.”

One caveat: Water temperature reports are from anglers and guides dipping hand-held thermometers, which might not be (and probably aren’t) completely accurate.

But they’re close and about all we have to rely on for that stretch of river.

If the heat kicks up runoff, that, too, could add cold water to the mix and affect the hatch.

Chris Eaton at Dragonfly Anglers in Crested Butte said high-country runoff has been in high gear, particularly where wind-blown dust coated the snowpack and increased snowmelt.

“We had a hot Memorial Day weekend and last week the Gunnison jumped up 700 cfs in one day,” Eaton said. “And the Lake Fork went up 1,000 or so in one day.”

He said “brown snow is all you can see in Paradise Divide” above Crested Butte.

And all that brown snow leads to the Gunnison.

Flows in the Black Canyon and Gunnison Gorge are controlled by the Aspinal dams, and this time of year water clarity below the East Portal is affected mostly by flows from the Cimarron River.

The Gunnison is “a bit off-color but you still can fish the canyon,” Burk said. “They’re running a lot of water (from the Cimarron) through the lower properties and I think a lot of people are irrigating their fields for the first time, so we’re getting some murk from that.”

But the actual runoff isn’t as much that key factor, other than from the aspect of wading comfort and safety, in the stonefly emergence as once thought.

It’s a player, for sure, but how much importance does it have?

“I don’t know,” said Burk. “What about phases of the moon? There are many factors to consider.”

But temperature, he maintains, is becoming something more and more important to consider.

Last year, the hatch around the Pleasure Park started and then stopped when cold rains put down the bugs.

“It wasn’t until the Chukar area it was normal and we hit it at Red Rocks and it was awesome,” Burk recalled. “But everyone down lower had a real spotty hatch.”

He said his guides on the Gunnison last week reported seeing stonefly nymphs “under every rock,” massing along the shore, waiting timelessly for the last key piece of this eternal puzzle.

“The nymphing should be stellar this weekend,” Burk said. “And if we get those high temperatures, I wouldn’t be surprised to see something major happen on the Gunnison this week.”

You can get the latest stonefly news by calling Cimarron Creek at 249-0408.